1. Field of the Invention
The present invention relates to a data communication apparatus, particularly to a data communication apparatus which has functions of selectively switching data communication and speech communication automatically.
2. Related Background Art
Traditionally, in a facsimile apparatus, etc. there are known systems for judging automatically voice communication and data communication in an automatic reception mode.
The followings systems are known for selectively switching data communication mode and voice communication mode automatically. First, an example for switching to the data communication mode after receiving a call will be described in reference to a facsimile apparatus.
1) In unautomatic reception mode, as soon as a call is received, facsimile procedure signals (NSF/CSI/DIS, etc.) are transmitted, and when response signals (e.g. NSS/TSI/DCS, etc.) are received, image communication is followed. If no response signals are received, a quasi-ring tone is issued to call for an operator for speech communication. But, in some apparatuses facsimile procedure signals are detected even after the calling of an operator. In U.S. Pat. No. 4,677,660, an apparatus of this kind is disclosed.
2) There is known a system having a message answering sequence at the time of starting a reception control, in addition to the above function. Such message as "If you wish speech communication, please wait for a while. If you wish data communication, please push the start button" is sent. This system has the advantage that a proper message can be given to a caller to teach subsequent procedures without fail.
3) Like the above system 1), as soon as a call is received in an automatic reception mode, facsimile procedure signals (NSF/CFI/DIS signals, etc.) are transmitted, and then corresponding response signals (e.g. NSS/TSI/DCS signals, etc.) are received. At the same time when these signals are detected, a speech signal and others from a partner are discriminated. When the speech signal is detected, the judgment is made that the partner is trying to make speech communication, and the speech communication mode is chosen at once. The facsimile procedure signals may be detected even after the calling of an operator. U.S. Pat. No. 4,815,121 is directed to a system in which a mode is switched by detection of a speech signal.
4) As in the system 2), a message answering function is added to the system 3). Usually, after detection of a speech signal from partner station, such message as "Calling now. Please wait for a while" is sent.
5) In the above systems 1)-4), a quasi-ring tone is used to call an operator. This system outputs a signal sent from a calling station through a speaker. At a called station, a message may not be issued through the speaker. U.S. Pat. No. 4,773,080 is an example of a system which issues a message through a speaker.
The following is a system for automatically changing from a speech communication mode to a data communication mode.
6) Upon reception of a call, a significant signal (e.g. CNG signal) from a partner station is detected, and if this signal is received, data communication is selected. U.S. patent application Ser. No. 573,684 (filed on Aug. 28, 1990) relates to a system which detects a CNG signal while sending a ring-back tone (quasi-reception tone) to the partner station at the time of the reception of a call. After transmission of this ring back tone, if no significant signal is detected after the lapse of a predetermined time period, an operator is called. This system gives priority to a speech communication mode since the ring back tone is always sent to a calling party after the reception of a call. A system for switching over a mode by detection of the CNG signal is disclosed in U.S. Pat. Nos. 4,800,439; 4,932,048; and 4,916,607.
However, in a conventional apparatus, data communication and speech communication are automatically switched over by one determined system regardless of communication condition.
For this reason, in automatic switchover from the data communication to the speech communication, unless a message response is made as in the above system 1), an operator may erroneously consider completion of dialing to a facsimile equipment and disconnect a line.
If a speech answering function is added, an apparatus is more expensive and communication time is always prolonged by the time corresponding to the message response.
In the case of a system (the above 6) in which priority is given to a speech communication mode and thereafter a mode is switched to data communication, there is a serious problem that polling transmission cannot be done. For instance, even if a call is received and CNG signal detection is executed while transmitting a ring-back tone, if the CNG signal is not detected when a calling station requests the polling because whether a mode is manual or automatic, the calling station is in a state of reception. So, it is impossible to shift to data communication and conduct the polling.